W.P. van Bennekom

Determination of mitomycin C in plasma, serum and urine by high-performance liquid chromatography with ultra-violet and electrochemical detection

The performance of a number of normal phase and reversed-phase systems, with ultraviolet detection at 360 nm, has been investigated with respect to their applicability to pharmacokinetic studies of mitomycin C (MMC). The reversed-phase system developed was also combined with a polarographic detector in order to compare the sensitivity and selectivity of ultraviolet and electrochemical detection. A simple isolation procedure, based on the adsorption of MMC on a non-ionogenic resin, has been developed. The developed assay is applied to a pharmacokinetic study from which some examples are given.

Hydrodynamic properties and mass transfer characteristics of electrochemical flow-through cells of the confined wall—jet type

Abstract The hydrodynamic properties and mass transfer characteristics of confined wall—jet electrochemical flow-through cells have been investigated for an electrochemically and chemically reversible, uncomplicated electrode reaction. Numerical as well as experimental results are presented. The approximate analytical solution for the stationary Sherwood number of a cell with a disk working electrode with radius R is: 〈Shj〉anal=0.924Re 1 3 d(d/b) 2 3 (d/R) 2 3 Sc 1 2 This relation is valid only when the diffusion boundary layer is small, creeping flow is assumed and the contribution of the impingement area to the signal can be neglected. Numerical correlations give the following solution for the mass transfer at a disk working electrode for Red values between 10 and 180; 1000 ⩽ Sc ⩽ 2000; 2 ⩽ R/d ⩽ 16.7 and 0.083 ⩽ b/d ⩽ 0.67 (reproduction of the solute at the auxiliary electrode is accounted for): 〈Shd〉num = 0.82Re0.36d(d/b)0.63(d/R) 2 3 Sc 1 3 For experimental verification a hydrodynamically optimized cell has been developed with a gold working electrode and a glassy carbon auxiliary electrode. For 10−3M potassium hexacyanoferrate(II) in 1 M potassium nitrate, the experimental results deviated less than 15% from the numerical solution when 8 ⩽ Red ⩽ 78; 0.083 ⩽ b/d ⩽ 0.67; Sc=1400 and R/d = 16.7.

Nitroprusside, antihypertensive drug and analytical reagent. Review of (photo)stability, pharmacology and analytical properties.

A review of physical, chemical, analytical and pharmacological properties of nitroprusside is presented. In view of the pharmaceutical applications of nitroprusside special attention is given to the discussion of the (photo)degradation, the stability of the pharmaceutical formulations, the application as a reagent in pharmaceutical analysis and the redox behaviour.

Determination of mitomycin C in human blood plasma and urine by high-performance differential pulse polarography

Abstract High-performance differential pulse polarography is used for determining the antitumor antibiotic mitomycin C in human blood plasma and urine. The limit of determination (2-ml samples) is 25 ng ml−1 when the substance is isolated by means of Amberlite XAD-2, and 200 ng mo−1 when samples are not pretreated. The method was applied in a pharmacokinetic experiment; no metabolites of mitomycin C were observed in urine or plasma.

High-performance pulse and differential pulse polarography: Part I. Theoretical considerations

Abstract A theoretical approach is given for complete elimination of the charging current caused by drop growth in modified normal and differential pulse polarography (n.p.p. and d.p.p.). Maximum sensitivity can be obtained in modified n.p.p., but the resolution of waves is better in modified d.p.p. or can be increased in differential modified n.p.p. The best overall performance can be achieved with modified d.p.p., considering sensitivity and wave resolution together. Preliminary results for the determination of chloramphenicol are described.

Determination of chloramphenicol at ultra-trace levels by high-performance differential pulse polarography: Application to Milk and Meat

Abstract High-performance differential pulse polarography (h.p.d.p.p.) is used to determine the antibiotic chloramphenicol. Optimum operating conditions are discussed. Calibration curves are linear from 10 ng ml -1 to 1 μg ml -1 ; the detection limit is about 3 ng ml -1 . Above 1 μg ml -1 , deviations from linearity occur, because of adsorption of chloramphenicol at the mercury electrode. A correction, based on variations in natural drop time, is suggested. Chloramphenicol is readily extracted from milk or minced meat with diethyl ether. The ether is evaporated, and the residue is taken up in acetate buffer pH 4.7 and filtered through a membrane filter. Recoveries from samples fortified at levels of 10–1000 ng ml -1 are about 60% for milk and 50% for minced meat.

Design and characterization of an electrochemical ring-disk flow-through detector for liquid chromatography

Abstract An electrochemical flow-through detector of the confined wall-jet type with a ring-disk electrode pair opposite the auxiliary electrode is described. The detector has a geometric cell volume of 2–8 μl, dependent on the spacer thickness used and is suitable for application in high-performance liquid chromatography (h.p.l.c.). The disk and ring currents depend on volumetric flow rate (ν), determined with hexacyanoferrate(II); currents are proportional to ν 0.331 (disk) and ν 0.230 (ring). Collection and shielding efficiency depends on cell geometry and flow rate. Collection efficiency lies in the range 20–65%, depending on electrode dimensions and spacer thickness, and becomes independent of flow rate at >0.25 ml min −1 . In a h.p.l.c. system, adrenaline is oxidized at the disk and the product is then reduced at the ring electrode. Calibration graphs are linear for the disk electrode (0.6–600 ng), and the ring electrode (6–600 ng). Reduction of oxygen at the ring-disk detector is discussed for aqueous media of pH 10.0, 5.0 and 3.5 and in methanol. In methanol, the ring current is small; in all solutions, the ring current is at least 100 times less than the disk current caused by dissolved oxygen. In a h.p.l.c. system with methanol as eluent, vitamin K 1 is reduced at the disk with, and the product is oxidized at the ring without, interference from oxygen in the eluent. The calibration graph (ring, collection mode) is linear for 10–1000 ng.

Polarography of disodium pentacyanonitrosylferrate(II) : Part 1. Pulse Polarographic Behaviour and Determination at Trace Levels

Abstract The pulse polarographic behaviour of disodium pentacyanonitrosylferrate(II) (sodium nitroprusside) was studied in the pH range 0–9. Maximum sensitivity is obtained in 1 M perchloric acid as a result of coincidence of the first two peaks and enhancement of the second peak. Calibration graphs are linear with conventional and high-performance differential pulse polarography at both the dropping mercury and static mercury drop electrode in the range 4–1000 ng ml −1 (1.3 × 10 −8 -3.3 × 10 −6 M). The estimated detection limits are about 2 ml −1 (7 × 10 −9 M). The reduction product(s) are probably adsorbed at the mercury electrode.

Fabrication and Characterisation of Leak-Tight Glassy Carbon Electrodes, Sealed in Glass Employing Silicon Coating, for Use in Electrochemical Detection

Abstract Glassy carbon discs have been coated with silicon in a chemical vapour deposition process to obtain leak-tight electrodes, sealed in glass. Electrodes with coatings thicker than 5μm prove to be leak-tight in contrast with uncoated ones. Silicon-coated electrodes show faster decay of charging current, less noise and decreased background current. Leak-tightness and electron microscope information correlate well with the electrochemical data. All results can be ascribed to the absence of a void between glassy carbon and glass at Si-coated electrodes. By silicon coating, signal-to-noise ratios are improved with a factor of about 5, as is demonstrated for catecholamines and metabolites in liquid chromatography with electrochemical detection.

Optimization criteria for a single bead-string reactor in flow injection analysis based on consecutive kinetic reactions

Abstract In flow-injection methods based on chemical reactions, simple one-step reactions are desirable, but more complex kinetics cannot always be avoided. The consecutive reaction considered here is A + reagent (s)→B→C. The response signal depends on the dispersion of the sample zone in the system and on the kinetics of the chemical reaction. The dispersion in a single-bead-string vector is described by the tanks-in-series model. The reaction of paracetamol with hexacyanoferrate (III) and phenol is used for experimental verification. Rules for optimum reactor design are given, the reactor length being used as the optimization parameter. Comparison of the experimental and calculated peak heights at different reactor lengths confirms the optimization rules.